As infrared light has a long penetration length to silicon (Si), it is necessary to elongate an optical path length in silicon when forming a high-sensitive sensor using near-infrared light. It is also necessary to form a potential for storing electrons obtained by photoelectrical conversion so as to reach a deeper position as photoelectric conversion occurs in a deeper position from a silicon surface on which light is incident.
As ion implantation with ultra-high energy is necessary for forming the potential in the deep position, there is a danger of increasing costs for development or manufacturing in related art. It is also necessary to develop resist correspond to the potential, which may increase difficulty level in development.
Accordingly, a method of forming photodiodes capable of sufficiently storing electrons photoelectrically converted by infrared light by performing ion implantation from the front-surface side and the back-surface side of a silicon substrate surface (a method in which ion implantation with ultra-high energy is not necessary) has been devised (for example, refer to JP-A-2010-192483 (Patent Document 1)).
In the method, first, photodiodes are formed on the surface of a silicon substrate in approximately the same depth as an image sensor corresponding to visible light by performing ion implantation from the front-surface side of the silicon substrate. After that, the silicon substrate is reversed and the back surface of the silicon substrate is polished. Then, ion implantation is performed from the back-surface side, thereby forming photodiodes on the back surface of the silicon substrate in approximately the same depth as the image sensor corresponding to visible light. A photoelectric conversion area having twice the depth at the maximum with respect to a depth direction is formed without performing ion implantation with ultra-high energy by applying the above manufacturing method.
The reversed silicon substrate is polished to have a necessary film thickness and ion is implanted, then, adhered to a support substrate for supporting the thickness of silicon after polishing. Then, an impurity which has been ion-implanted from the back-surface side of the silicon substrate is activated by high-temperature activation processing.